U.S. Pat. Nos. 5,048,557, 5,090,442, and 4,527,593 are each incorporated herein by reference into this disclosure.
The present invention relates generally to a battery refill system used for filling battery cells to a predetermined level and for automatically monitoring and maintaining the battery cells at that level. More particularly, the present invention defines the material parameters of tubing which has found a particularly advantageous use within the battery refill system. This tubing may be used with any of the inventions, and particularly the refill valves, disclosed in U.S. Pat. Nos. 5,048,557 and 5,090,442.
It is standard practice in the field of industrial battery watering to use a flexible polyvinyl chlorine ("PVC") thermoplastic tubing to interconnect automatic shut-off valves (such as those disclosed in U.S. Pat. Nos. 5,048,557 and 5,090,442) which are mounted on each cell of a battery to be filled within a battery watering system. The watering system is intended to last the life of the battery (five years or longer). A common water supply feeds water to each cell through the thermoplastic tubing.
It has been widely observed that the thermoplastic tubing mounted on such battery cells tends to discolor, soften, and tactify with age. It was assumed that the softening was generally insignificant and that the discoloration and tactification were due to acid fumes and electrolyte migration occurring during the battery charging cycle. However, these thermoplastic tubing characteristics were not perceived as problems which would affect the reliability of the watering system, so long as no leakage occurred within the tubing. While it was felt that acid fumes and electrolyte migration might cause refill valves to lock in an open or closed position, the mechanism by which this occurred was not completely understood. In fact, it was previously understood that it was the evaporation of the fluid used to fill the battery cells which left a sticky residue between the main valve and seat, such as might create a premature shut-off condition (see U.S. Pat. No. 5,048,557).
A primary reason automatic watering systems are not more widely used is their susceptibility to apparent random failure due to valve contamination. It has been assumed that the specific source of the contamination is either sticky residue from the inside of the battery cells migrating into the valves, or contaminants carried by the water supply into the valve by the thermoplastic tubing.
It is now understood that PVC thermoplastic tubing deteriorates in a fashion which is particularly damaging to the refill valves used in a battery watering system. Specifically, it has been experimentally determined that the tactification found to occur within the thermoplastic tubing after a relatively short period of service on the top of the battery is not simply acid residue collecting on the tubing surface; rather, it is caused-by a separation of the plasticizer found within such tubing from the plastic resin. This plasticizer "bleeding" allows the plasticizer to collect as a liquid on both the inside and the outside of the tubing. Further, it has been found that this plasticizer is immiscible in water, but migrates under the shear stress of the flowing water into the battery cell refill valves. This sticky plasticizer coats critical valve members and can cause malfunctions.